Print circuit board, optical module, and optical transmission equipment

ABSTRACT

Provided is a print circuit board including: a ground conductor layer; a pair of strip conductors extending along a first orientation; a first resonator conductor three-dimensionally intersecting with the pair of strip conductors along a second orientation; a pair of first via holes connecting the first resonator conductor and the ground conductor layer; and a dielectric layer including the first resonator conductor therein, and being disposed between the ground conductor layer and the pair of the strip conductors. A distance H 1  between the pair of strip conductors and the ground conductor layer is twice or more a distance H 2  between the pair of strip conductors and the first resonator conductor, and a line length L of the first resonator conductor is 0.4 wavelength or more and 0.6 wavelength or less at a frequency corresponding to the bit rate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/835,532, filed Dec. 8, 2017, which claims priority from Japaneseapplication JP 2016-245394, filed on Dec. 19, 2016, the content contentsof which are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a print circuit board, an opticalmodule, and an optical transmission equipment, and in particular, to theprint circuit board in which unnecessary electromagnetic wavespropagating to a differential transmission line of a micro-strip linetype are suppressed.

2. Description of the Related Art

In a print circuit board, a differential transmission line transmittinga serial data signal may be formed in some cases. Unnecessary highfrequency noise may occur in such a differential transmission line.

For such high frequency noise, a method of selectively inhibitingconduction propagation of a common mode signal component without havinga bad influence on the differential signal component conducting andpropagating the differential transmission line (without deterioratingdifferential signal quality) has been proposed. WO 2011/004453 A1 and JP2012-227887A disclose a configuration in which a resonator is connectedto a ground conductor layer through a via hole in which a rectangularconductor film is disposed at the center thereof, and the resonator iscoupled by disposing the resonator below the differential transmissionline. In US 2011/0298563 A1 discloses a configuration in which aresonator is configured by providing a plurality of spiral openingportions (slots) in the ground conductor layer and disposing the openingportions on both sides of the differential transmission line to connectboth portions at opening portion on the line, and the resonator iscoupled to a differential transmission line.

SUMMARY OF THE INVENTION

It is desirable to selectively inhibit conduction propagation of thecommon mode signal component transmitted to a differential transmissionline in a desired frequency domain. Therefore, it is conceivable tocouple a resonator structure to the differential transmission line.Here, the resonator structure is configured to include a groundconductor layer, a resonator conductor, and a pair of via holesconnecting the resonator conductor and the ground conductor layer.However, the resonator conductor and the pair of the via holes areformed in separate steps. Therefore, due to a positional deviation ofthe pair of the via holes with respect to the resonator conductor, afrequency domain of a common mode signal component which can beinhibited varies. If it is difficult to selectively inhibit theconduction propagation of the common mode signal component in thedesired frequency domain due to variation of the frequency domain, theyield is reduced.

The present invention has been made in view of the above problems, andit is an object to provide a print circuit board, an optical module, andan optical transmission equipment which can selectively inhibittransmission propagation of a common mode signal component to adifferential transmission line.

(1) According to an aspect of the present invention, there is provided aprint circuit board including a ground conductor layer, a pair of stripconductors that is disposed on a board surface side in a laminationorientation of the ground conductor layer and extends along a firstorientation, a first resonator conductor that is disposed between theground conductor layer and the pair of the strip conductors, andthree-dimensionally intersects with the pair of strip conductors along asecond orientation intersecting the first orientation, a pair of firstvia holes that respectively connects the first resonator conductor andthe ground conductor layer, and a dielectric layer that includes thefirst resonator conductor therein, and is disposed between the groundconductor layer and the pair of the strip conductors, in which in adifferential transmission line of a micro-strip line type in which adigital modulation signal is transmitted is configured to include theground conductor layer, the pair of the strip conductors, and thedielectric layer, a first resonator structure is configured to includethe ground conductor layer, the first resonator conductor, and the pairof first via holes, a distance H₁ along the lamination orientationbetween the pair of strip conductors and the ground conductor layer istwice or more a distance H₂ along the lamination orientation between thepair of strip conductors and the first resonator conductor, and in thefirst resonator conductor, a line length L of the first resonatorconductor from the center position of one via hole of the pair of firstvia holes to the center position of the other via hole is 0.4 wavelengthor more and 0.6 wavelength or less at a frequency corresponding to thebit rate of the digital modulation signal to be transmitted.

(2) In the print circuit board according to (1), the first resonatorconductor may extend from each of the pair of first via holes to any oneof the inside and the outside of the first resonator conductor along thesecond orientation.

(3) In the print circuit board according to (1), the first resonatorconductor may extend from each of the pair of first via holes to any oneof the inside and the outside of the first resonator conductor along thesecond orientation, and further bend in any one direction of the firstorientation.

(4) In the print circuit board according to (1), the first resonatorconductor may extend outward along the second orientation from a portionin which the first resonator conductor three-dimensionally intersectswith the pair of strip conductors, bend in any one direction of thefirst orientation, further extend along the first orientation, bends tothe outside in the second orientation, and extend along any one of theoutside and the inside along the second orientation to connect with thepair of first via holes.

(5) In the print circuit board according to any one of (1) to (4), thefirst resonator conductor may have a shape that is substantially linesymmetric with respect to the pair of strip conductors in a plan view.

(6) In the print circuit board according to any one of (1) to (5),further including a second resonator conductor that is disposed in thesame layer as the first resonator conductor, and three-dimensionallyintersects with the pair of strip conductors along the secondorientation, and a pair of second via holes that respectively connectsthe second resonator conductor and the ground conductor, a secondresonator structure may be configured to include the ground conductorlayer, the second resonator conductor, and the pair of second via holes,and in the second resonator conductor, a line length L of the secondresonator conductor from the center position of one via hole of the pairof second via holes to the center position of the other via hole may be0.4 wavelength or more and 0.6 wavelength or less at a frequencycorresponding to the bit rate of the digital modulation signal to betransmitted.

(7) In the print circuit board according to (4), further including asecond resonator conductor that is disposed in the same layer as thefirst resonator conductor, and three-dimensionally intersects with thepair of strip conductors along the second orientation, and a pair ofsecond via holes that respectively connects the second resonatorconductor and the ground conductor, a second resonator structure may beconfigured to include the ground conductor layer, the second resonatorconductor, and the pair of second via holes, in the second resonatorconductor, a line length L of the second resonator conductor from thecenter position of one via hole of the pair of second via holes to thecenter position of the other via hole may be 0.4 wavelength or more and0.6 wavelength or less at a frequency corresponding to the bit rate ofthe digital modulation signal to be transmitted, and the secondresonator conductor may extend outward along the second orientation froma portion in which the second resonator conductor in parallel with thefirst resonator conductor three-dimensionally intersects with the pairof strip conductors, bend in the other direction of the firstorientation, further extend away from the first resonator conductoralong the first orientation, bend to the outside in the secondorientation, and extend along anyone of the outside and the inside alongthe second orientation to connect with the pair of second via holes.

(8) According to another aspect of the present invention, there isprovided a print circuit board including a ground conductor layer, apair of strip conductors that is disposed on a board surface side in alamination orientation of the ground conductor layer and extends along afirst orientation, a first resonator conductor that is disposed on theboard surface side in a lamination orientation of the pair of stripconductors, and three-dimensionally intersects with the pair of stripconductors along a second orientation intersecting the firstorientation, a pair of first via holes that respectively connects thefirst resonator conductor and the ground conductor layer, and adielectric layer that includes the pair of strip conductors therein, andis disposed between the ground conductor layer and the first resonatorconductor, a differential transmission line of a micro-strip line typein which a digital modulation signal is transmitted may be configured toinclude the ground conductor layer, the pair of the strip conductors,and the dielectric layer, a first resonator structure may be configuredto include the ground conductor layer, the first resonator conductor,and the pair of first via holes, a distance H₁ along the laminationorientation between the pair of strip conductors and the groundconductor layer may be twice or more a distance H₂ along the laminationorientation between the pair of strip conductors and the first resonatorconductor, and in the first resonator conductor, a line length L of thefirst resonator conductor from the center position of one via hole ofthe pair of first via holes to the center position of the other via holemay be 0.4 wavelength or more and 0.6 wavelength or less at a frequencycorresponding to the bit rate of the digital modulation signal to betransmitted.

(9) In the print circuit board according to any one of (1) to (8), anangle between the first orientation and the second orientation may be85° or more and 90° or less.

(10) In the print circuit board according to any one of (1) to (9), thefirst orientation and the second orientation may be substantiallyorthogonal to each other.

(11) According to still another aspect of the present invention, thereis provided an optical module including the print circuit boardaccording to any one of (1) to (10), the print circuit board further mayinclude an IC that drives the digital modulation signal.

(12) In the optical module according to (11), a metal housing thatcovers the print circuit board to configure an electromagnetic shield,and includes an opening portion for exposing a portion of the printcircuit board to an outside may be further included.

(13) According to still another aspect of the present invention, thereis provided an optical transmission equipment on which the opticalmodule according to (11) or (12) may be mounted.

(14) According to still another aspect of the present invention, thereis provided an optical transmission equipment including the printcircuit board according to any one of (1) to (10), the print circuitboard may further include an IC that drives the digital modulationsignal.

According to the present invention, a print circuit board, an opticalmodule, and an optical transmission equipment which can selectivelyinhibit transmission propagation of a common mode signal component to adifferential transmission line are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a configuration of an opticaltransmission equipment and an optical module according to a firstembodiment of the present invention.

FIG. 2 is a schematic view illustrating a flat surface of a portion of aprint circuit board according to the first embodiment of the presentinvention.

FIG. 3 is a schematic view illustrating a cross section of the portionof the print circuit board according to the first embodiment of thepresent invention.

FIG. 4 is a diagram illustrating characteristics of a differentialtransmission line according to the first embodiment of the presentinvention.

FIG. 5 is a schematic perspective view illustrating an external shape ofan optical module according to the first embodiment of the presentinvention.

FIG. 6 is a schematic perspective view illustrating the structure of theoptical module according to the first embodiment of the presentinvention.

FIG. 7 is a schematic view illustrating a flat surface of a portion of aprint circuit board according to a second embodiment of the presentinvention.

FIG. 8 is a diagram illustrating characteristics of a differentialtransmission line according to the second embodiment of the presentinvention.

FIG. 9 is a schematic view illustrating the flat surface of the portionof the print circuit board according to the second embodiment of thepresent invention.

FIG. 10 is a diagram illustrating characteristics of the differentialtransmission line according to the second embodiment of the presentinvention.

FIG. 11 is a schematic view illustrating a flat surface of a portion ofa print circuit board according to a third embodiment of the presentinvention.

FIG. 12 is a diagram illustrating characteristics of a differentialtransmission line according to the third embodiment of the presentinvention.

FIG. 13 is a schematic view illustrating a structure of a portion of aprint circuit board according to a fourth embodiment of the presentinvention.

FIG. 14 is a schematic view illustrating a structure of a portion of aprint circuit board according to a fifth embodiment of the presentinvention.

FIG. 15 is a schematic view illustrating a structure of a portion of aprint circuit board according to a sixth embodiment of the presentinvention.

FIG. 16 is a schematic view illustrating a structure of a portion of aprint circuit board according to a seventh embodiment of the presentinvention.

FIG. 17 is a schematic view illustrating a cross section of the portionof the print circuit board according to the seventh embodiment of thepresent invention.

FIG. 18 is a schematic view illustrating a flat surface of a portion ofa print circuit board according to a comparative example of the firstembodiment of the present invention.

FIG. 19 is a diagram illustrating characteristics of a differentialtransmission line according to the comparative example of the firstembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be describedspecifically and in detail with reference to the drawings. In all thedrawings for describing the embodiments, the same reference numerals aregiven to the members having the same function, and the repeateddescription thereof will be omitted. The drawings illustrated belowmerely illustrate examples of the embodiments, and the sizes of thedrawings and the scales described in the embodiments do not necessarilycoincide with each other.

First Embodiment

FIG. 1 is a schematic view illustrating a configuration of an opticaltransmission equipment 1 and an optical module 2 according to a firstembodiment of the present invention. The optical transmission equipment1 includes a print circuit board 11. In addition, the optical module 2includes a print circuit board 21. The print circuit board according tothe first embodiment is one or both of the print circuit boards 11 and21.

The optical transmission equipment 1 further includes an IC 12. Theoptical transmission equipment 1 is, for example, a large-capacityrouter or a switch. The optical transmission equipment 1 has, forexample, a function of a switching equipment, and is disposed in a basestation or the like. The optical transmission equipment 1 acquires datafor receiving (electric signal for receiving) from the optical module 2,determines to transmit what data to where using the IC 12 or the like,generates data for transmitting (electric signal for transmitting), andtransmits the data to the corresponding optical module 2 through theprint circuit board 11.

The optical module 2 is a transceiver having a function of opticaltransmitting and a function of optical receiving, and includes a ROSA23A which converts an optical signal received through an optical fiber3A into an electric signal, and a TOSA 23B which converts an electricsignal to an optical signal and transmits the optical signal to anoptical fiber 3B. The print circuit board 21, the ROSA 23A and the TOSA23B are connected to each other through flexible boards 22A and 22B(flexible printed circuit: FPC), respectively. An electric signal istransmitted from the ROSA 23A to the print circuit board 21 through theflexible board 22A, and an electric signal is transmitted from the printcircuit board 21 to the TOSA 23B through the flexible board 22B. Theoptical modules 2 and the optical transmission equipment 1 are connectedto each other through an electrical connector 5. The ROSA 23A and theTOSA 23B are electrically connected to the print circuit board 21 andare optical elements that convert from one to the other of opticalsignals or electric signals.

A transmission system according to the first embodiment includes two ormore of the optical transmission equipment 1, two or more of the opticalmodules 2, and one or more of optical fibers 3. Each opticaltransmission equipment 1 is mounted on one or more of the opticalmodules 2. The optical fiber 3 is connected between the optical modules2 mounted on the two optical transmission equipments 1, respectively.Transmission data generated by one of the optical transmission equipment1 is converted into an optical signal by the mounted optical module 2,and such an optical signal is transmitted to the optical fiber 3. Theoptical signal transmitted over the optical fiber 3 is received by theoptical module 2 mounted on the other optical transmission equipment 1,and the optical module 2 converts the optical signal into an electricsignal and transmits the electric signal to the other opticaltransmission equipment 1 as reception data.

Here, the bit rate of the electric signal transmitted and received byeach of the optical modules 2 is 100 Gbit/s class, and the opticalmodule 2 has a multi-channel system of 4 channels for transmitting and 4channels for receiving. The bit rate of the electric signal transmittingeach channel is any one of 25 Gbit/s to 28 Gbit/s, specifically, the bitrate of the electric signal transmitting each channel is 25.78 Gbit/s. Adifferential transmission line is a line for propagating an electricalserial data signal with a bit rate of 25.78 Gbit/s.

FIG. 2 is a schematic view illustrating a flat surface of a portion of aprint circuit board 31 according to the first embodiment. FIG. 3 is aschematic view illustrating a cross section of the portion of the printcircuit board 31 according to the first embodiment. FIGS. 2 and 3schematically illustrate the flat surface and the cross section,respectively, in order to understand the structure of the print circuitboard 31, so that the actual plan view and sectional view are differentfrom each other. The print circuit board 31 is a print wiring boardhaving a multilayer structure in which a plurality of conductor layersare formed through each of dielectric layers, and in FIGS. 2 and 3, aportion of the print circuit board 31 in which the differentialtransmission line and the resonator structure are formed (only the upperportion) is illustrated among the multilayer structure. FIG. 3illustrates a cross section taken along line III-III illustrated in FIG.2.

The print circuit board 31 according to the first embodiment has aplurality of differential transmission lines for high speed digitalsignals, and the print circuit board 31 has a plurality of channels. InFIGS. 2 and 3, one differential transmission line 32 (one channel) amongthe plurality of differential transmission lines is illustrated. Here,the bit rate of the electric signal transmitted to the differentialtransmission line 32 is 25.78 Gbit/s. Here, the print circuit board 31is the print circuit board 21 of the optical module 2, but as describedabove, the print circuit board 11 of the optical transmission equipment1 may be used.

As illustrated in FIGS. 2 and 3, the print circuit board 31 is providedwith a dielectric layer 100, a pair of strip conductors 101 and 102, aground conductor layer 103, a first resonator conductor 104, and a pairof first via holes 105 a, and 105 b. Although on the uppermost surfaceillustrated in FIG. 2, a protective dielectric film 107 is disposed overthe entire surface, in order to facilitate understanding of themultilayer structure of the print circuit board 31, the protectivedielectric film 107 is omitted. In addition, similarly, the dielectriclayer 100 is not illustrated in FIG. 2.

In the dielectric layer 100, a material (glass epoxy resin) including aglass cloth substrate and an epoxy resin is used. For example, therelative dielectric constant of the dielectric layer 100 is 3.5. Thedielectric layer 100 includes the first resonator conductor 104 therein,and is disposed between the pair of strip conductors 101 and 102 and theground conductor layer 103.

The pair of strip conductors 101 and 102 are disposed on the boardsurface side (upper side in FIG. 3) in the lamination orientation of theground conductor layer 103, and both extend along a first orientation(vertical orientation illustrated in FIG. 2). The pair of stripconductors 101 and 102 are formed on the uppermost metal layer of themultilayer structure of the print circuit board 31. The pair of stripconductors 101 and 102 are copper foils having a thickness of 37 μm. Awidth W of the pair of strip conductors 101 and 102 is 0.17 mm, and aninterval G between the pair of strip conductors 101 and 102 is 0.20 mm.Here, the interval G is the distance from the inner edge of the stripconductor 101 to the inner edge of the strip conductor 102. It isdesirable that the pair of strip conductors 101 and 102 are spaced apartfrom each other by the interval G, have the width W, and extend in alinear shape in the first orientation in parallel with each other.However, the shapes of the pair of strip conductors 101 and 102 may bebent or the like, depending on the relationship with other componentsmounted on the print circuit board 31. Even in such a case, in a regionthree-dimensionally intersecting with the first resonator conductor 104and a region in the vicinity thereof, the shape may be a parallel linearshape. A planar shape of the pair of strip conductors 101 and 102 isprocessed and formed by patterning.

The ground conductor layer 103 is a copper foil with a thickness of 18μm and is a third metal layer counted from the front surface side amongthe multilayer structure of the print circuit board 31. As illustratedin FIG. 3, the distance H₁ between the pair of strip conductors 101 and102 and the ground conductor layer 103 is 166 μm. Here, the distance H₁between the pair of strip conductors 101 and 102 and the groundconductor layer 103 is the distance between the lower surface of thepair of strip conductors 101, 102 and the upper surface of the groundconductor layer 103. The differential transmission line 32 of amicro-strip line type, through which a digital modulation signal istransmitted is configured by the dielectric layer 100, the pair of stripconductors 101 and 102, and the ground conductor layer 103. Thecharacteristic impedance of the differential transmission line 32 in thedifferential mode can be made 100Ω. Although it is desirable that theground conductor layer 103 is disposed over the entire surface of theprint circuit board 31, the ground conductor layer 103 may have a shapeincluding a region below the pair of strip conductors 101 and 102 andthe first resonator conductor 104 and extending to both sides in thesecond orientation. The second orientation is an orientationintersecting the first orientation.

The first resonator conductor 104 is disposed between the pair of stripconductors 101 and 102 and the ground conductor layer 103. The firstresonator conductor 104 is a copper foil with a thickness of 36 μm andis a second metal layer counted from the front surface side among themultilayer structure of the print circuit board 31. As illustrated inFIG. 3, the distance H₂ between the pair of strip conductors 101 and 102and the first resonator conductor 104 is 65 μm. Here, the distance H₂between the pair of strip conductors 101 and 102 and the first resonatorconductor 104 is the distance between the lower surface of the pair ofstrip conductors 101, 102 and the upper surface of the first resonatorconductor 104. It is desirable that the distance H₁ is twice or more thedistance H₂, and the print circuit board 31 according to the firstembodiment satisfies such a condition.

The first resonator conductor 104 three-dimensionally intersects withthe pair of strip conductors 101 and 102 along the second orientation.It is desirable that the angle between the first orientation and thesecond orientation is 85° or more and 90° or less, and it is furtherdesirable that the first orientation and the second orientation aresubstantially orthogonal to each other (angle formed is 90°). In thefirst embodiment, the first orientation (vertical orientation in FIG. 2)and the second orientation (horizontal orientation in FIG. 2) areorthogonal to each other. The first resonator conductor 104 is providedwith land portions 110 a and 110 b (via lands) each having a circularshape (diameter: 0.45 mm) at both ends thereof.

The pair of first via holes 105 a and 105 b (circular shape) arerespectively disposed so that the center of the circular shape isideally penetrated through the center of the circular shape of the landportions 110 a and 110 b. Each of the pair of first via holes 105 a and105 b is a cylindrical through hole having a diameter of 0.20 mm, and ametal is disposed on the inner wall of the through hole. The distance Dbetween the centers of the pair of first via holes 105 a and 105 b is2.0 mm. A circular hole (through hole) is formed in the dielectric layer100 by a drill step so as to extend from the pair of strip conductors101 and 102 (uppermost metal layer) to the ground conductor layer 103(third metal layer) perpendicular to the planar direction of the printcircuit board 31, and the pair of first via holes 105 a and 105 b areformed by copper plating in the inner wall (inside surface) of the hole.The pair of first via holes 105 a and 105 b connect the first resonatorconductor 104 (land portions 110 a and 110 b at the both ends of) andthe ground conductor layer 103, respectively. A first resonatorstructure is configured to include the ground conductor layer 103, thefirst resonator conductor 104, and the pair of first via holes 105 a and105 b.

As illustrated in FIGS. 2 and 3, the protective dielectric film 107 isthe uppermost layer of the print circuit board 31 and is disposed so asto cover the pair of strip conductors 101 and 102 and the dielectriclayer 100. The protective dielectric film 107 is a dielectric filmcalled a solder resist for preventing adhesion of solder and has athickness of approximately 40 μm. The protective dielectric film 107 maynot be disposed unless otherwise required.

The first feature of the print circuit board 31 according to the firstembodiment lies in the shape of the first resonator conductor 104. Thesecond feature is that the distance H₁ is twice or more the distance H₂.Hereinafter, the shape of the first resonator conductor 104 will bedescribed. The planar shape of the first resonator conductor 104 isprocessed and formed by patterning.

The first resonator conductor 104 extends in a linear shape from each of(centers of) the land portions 110 a and 110 b at both ends along thesecond orientation to the inside of the first resonator conductor 104.That is, the first resonator conductor 104 extends from each of (centersof) the pair of first via holes 105 a and 105 b along the secondorientation to the inside of the first resonator conductor 104. Here,the description of “to extend to the inside of the first resonatorconductor 104” means to extend in an orientation approaching from bothsides with respect to the pair of strip conductors 101 and 102 withwhich the first resonator conductor 104 three-dimensionally intersects.The description of “to extend to the outside of the first resonatorconductor 104” means to extend in an orientation away from both sideswith respect to the pair of strip conductors 101 and 102 with which thefirst resonator conductor 104 three-dimensionally intersects. Actually,the planar shape of the first resonator conductor 104 and the pair offirst via holes 105 a and 105 b are formed in separate steps, so thatthe positional deviation occurs between (centers of) the land portions110 a and 110 b and (centers of) the pair of the first via holes 105 aand 105 b, respectively. Here, the positional deviation amount is 0.125mm. The diameter 0.45 mm of the land portions 110 a and 110 b is a valuethat can correspond to the diameter 0.20 mm of the pair of first viaholes 105 a and 105 b and the positional deviation amount of 0.125 mm.In addition, among the first resonator conductors 104, the width W₁ ofthe portion extending in a linear shape (excluding the bent portion) is0.20 mm.

Here, the description of “first resonator conductor 104 extends alongthe second orientation from each of the land portions 110 a and 110 b orfrom each of the pair of first via holes 105 a and 105 b” allows atolerance in positional deviation on manufacturing, so that the centerof the linear shape portion of the first resonator conductor 104 may notstrictly extend from the center of the land portions 110 a and 110 b,and the extending orientation of the linear shape may be along thesecond orientation and may not be strictly parallel to the secondorientation. In this specification, the description of “along the firstorientation (or the second orientation)” is the same.

It is desirable that both of the first resonator conductor 104 accordingto the first embodiment extend along the second orientation from bothends thereof (land portions 110 a and 110 b) or from each of the pair offirst via holes 105 a and 105 b to the inside of the first resonatorconductor 104, and that both further bend in any one direction in thefirst orientation (downward in FIG. 2). Furthermore, it is desirablethat both extend to the inside of the first resonator conductor 104along the second orientation, and reach the portions three-dimensionallyintersecting with the pair of strip conductors 101 and 102. That is, itis desirable that the first resonator conductor 104 extends to theoutside along the second orientation from the portionsthree-dimensionally intersecting with the pair of strip conductors 101and 102, bends in any one direction in the first orientation (upward inFIG. 2), further extends along the first orientation, bends to theoutside in the second orientation, and extends to the outside along thesecond orientation to connect with the pair of first via holes.

The first resonator conductor 104 according to the first embodiment hasa shape extending to the inside along the second orientation from theland portions 110 a and 110 b disposed at both ends thereof. Since thefirst resonator conductor 104 has such a shape, it is possible tosuppress degradation of characteristics due to the positional deviationbetween the land portions 110 a and 110 b and the pair of first viaholes 105 a and 105 b. Details of the effect will be described later. Inaddition, the first resonator conductor 104 according to the firstembodiment has a shape connected to the pair of strip conductors 101 and102 extending along the first orientation, and to the land portions 110a and 110 b which three-dimensionally intersect along the secondorientation, respectively extend along the second orientation from aportion three-dimensionally intersects, repeat bending and stretching,and are disposed at both ends thereof. Since the first resonatorconductor 104 according to the first embodiment has such a shape, a linelength L of the first resonator conductor 104 from the center positionof one via hole (for example, via hole 105 a) of the pair of first viaholes to the center position of the other via hole (for example, viahole 105 b) is 3.4 mm. Here, the line length L is the length of thecenter line of the linear shape in which the first resonator conductorextends, and in the bent portion, the line length L may be calculatedbased on the center line of the linear shape respectively extending toboth sides. As illustrated in FIG. 2, the length L₁ of the center lineof the linear shape portion extending in the first orientation of thefirst resonator conductor 104 is 0.7 mm. That is, considering the centerline, it is possible to dispose the first resonator conductor 104 havinga long line length of 3.4 mm in a small region of 0.7 mm along the firstorientation. In addition, it is possible to provide one linear shapeportion of 0.7 mm along the first orientation on both sides (two intotal), so that these two linear shape portions serve as a detour route,and the linear shape portion along the second orientation can beshortened.

The first resonator conductor 104 is disposed inside the dielectriclayer 100 having a relative dielectric constant ε_(r) of 3.5, and awavelength shortening ratio (1/√ε_(r)) of the dielectric layer 100 withrespect to a vacuum is 0.535. One wavelength λg of the first resonatorconductor 104 at a frequency of 25.78 GHz corresponding to the bit rateis calculated to be 6.22 mm. Therefore, the line length L of 3.4 mm ofthe first resonator conductor 104 is 0.55 λg in terms of the wavelengthλg. In a case of changing the shape of the first resonator conductor104, in a case of changing the distance between the first resonatorconductor 104 and the ground conductor layer 103, and in a case ofchanging the material of the dielectric layer 100, an appropriate valueof the line length L of the first resonator conductor 104 may beselected according to the case. The appropriate value can be obtainedby, for example, an electromagnetic field analysis tool, and desirablyhas a length of 0.4 wavelength or more and 0.6 wavelength or less at afrequency corresponding to the bit rate of the digital modulationsignal. Here, the bit rate is 25.78 Gbit/s, and the frequencycorresponding to the bit rate is 25.78 GHz. That is, the frequencycorresponding to the bit rate of the digital modulation signal isobtained by changing the unit to Hz with the numerical value of the bitrate (unit bit/s) unchanged.

It is desirable that the first resonator conductor 104 has a shape thatis substantially line symmetrical with respect to the pair of stripconductors 101 and 102 in a plan view. Here, the description of “to beline symmetrical with respect to the pair of strip conductors 101 and102” means to be line symmetrical with respect to the center line of thepair of strip conductors 101 and 102 (center line of the strip conductor101 and center line of the strip conductor 102). It is desirable toreduce the influence on the conduction propagation of the differentialsignal component transmitted to the differential transmission line.Therefore, it is desirable that the resonator structure is symmetricalwith respect to the pair of strip conductors 101 and 102.

FIG. 4 is a diagram illustrating characteristics of a differentialtransmission line 32 according to the first embodiment. FIG. 4 is agraph illustrating the frequency dependence of the differential modepass characteristic (Sdd21), differential mode reflection characteristic(Sdd11 and Sdd22), and common mode pass characteristic (Scc21) in thedifferential transmission line 32. Since the first resonator conductor104 (first resonator structure) three-dimensionally intersects with thepair of strip conductors 101 and 102 (differential transmission line32), deterioration (increase) occurs in the differential mode reflectioncharacteristic (Sdd 11 and Sdd 22), but it is a value of −20 dB or lessin the frequency range of 0 to 30 GHz, and a relatively favorable valueis maintained. This is considered to be due to the fact that the firstresonator conductor 104 has a narrow linear shape with a width W₁ of0.20 mm, and the area which three-dimensionally intersects with the pairof strip conductors 101 and 102 (facing area, and overlapping area in aplan view) is reduced.

In addition, the differential mode pass characteristic (Sdd 21)illustrates favorable characteristics. On the other hand, in the commonmode pass characteristic (Scc 21), an attenuation region centered at thefrequency 26.3 GHz is generated, and conduction propagation of thecommon mode signal component of the frequency 25.78 GHz can be inhibitedby approximately 10 dB.

FIG. 18 is a schematic view illustrating a flat surface of a portion ofa print circuit board 331 according to a comparative example of thefirst embodiment. FIG. 19 is a diagram illustrating characteristics of adifferential transmission line 32 according to the comparative example,and illustrates the common mode pass characteristic (Scc 21) in a casewhere the positional deviation Δy is +0.125 mm, 0, and −0.125 mm,respectively. The print circuit board 331 according to the comparativeexample has the same structure except that the shape of the firstresonator conductor 304 is different from the shape of the firstresonator conductor 104 according to the first embodiment. The firstresonator conductor 304 according to the comparative example extendsalong any one direction in the first orientation (downward asillustrated in FIG. 12) from land portions 310 a and 310 b disposed atthe both ends, extends to the inside of the first resonator conductor304 along the second orientation, and reaches the portion thatthree-dimensionally intersects with the pair of strip conductors 101 and102. The distance D between the centers of the pair of first via holes105 a and 105 b is 1.4 mm, and the line length L of the first resonatorconductor 304 from the center position of the via hole 105 a to thecenter position of the via hole 105 b is 3.2 mm. Since the firstresonator conductor 304 has such a shape, in a case where the centerpositions of the pair of first via holes 105 a and 105 b are disposed atthe center positions of the land portions 310 a and 310 b, respectively,the characteristics of a differential transmission line 332 are similarto the characteristics of the differential transmission line 32illustrated in FIG. 4.

Next, the influence of characteristics due to the positional deviationof the pair of first via holes 105 a and 105 b with respect to the firstresonator conductor 104 (or 304) between the differential transmissionline 32 according to the first embodiment and the differentialtransmission line 32 according to the comparative example will beexamined. As described above, the pair of first via holes 105 a and 105b having the positional deviation amount of 0.125 mm may vary by ±0.125mm maximum with respect to the first resonator conductor 104 (or 304) ineach of the first orientation and the second orientation. As describedabove, since the first resonator conductor 104 (or 304) and the pair offirst via holes 105 a and 105 b are formed in separate steps,respectively, the relative position between the first resonatorconductor 104 (or 304) and the pair of first via holes 105 a and 105 bvaries. However, since the planar shape of the first resonator conductor104 is formed by patterning, the relative positional variations of theland portions 110 a and 110 b (or 310 a and 310 b) of the firstresonator conductor 104 (or 304) are significantly small. Similarly,since the pair of first via holes 105 a and 105 b are formed by a commondrilling step, the relative positional variations (distance D betweenthe centers) of the pair of first via holes 105 a and 105 b aresignificantly small.

First, regarding the comparative example, the positional deviation Δy ofthe pair of first via holes 105 a and 105 b (each center position) withrespect to the land portions 310 a and 310 b (each center position)along the first orientation (vertical orientation illustrated in FIG.18) will be considered. The positional deviation Δy=0 is a case wherethe center position of each of the pair of first via holes 105 a and 105b coincides with the center position of each of the land portions 310 aand 310 b. The positional deviation Δy=+0.125 mm is a case where thecenter position of each of the pair of first via holes 105 a and 105 bis deviated upward as illustrated in FIG. 18 from the center position ofeach of the land portions 310 a and 310 b. The positional deviationΔy=−0.125 mm is a case where the center position of each of the pair offirst via holes 105 a and 105 b is deviated downward as illustrated inFIG. 18 from the center position of each of the land portions 310 a and310 b. In the first resonator conductor 304 depending on the comparativeexample, the line length L varies according to the positional deviationΔy along the first orientation. The line length L when positionaldeviation Δy=+0.125 mm is 0.25 mm longer than the line length L whenΔy=0, the line length L when Δy=−0.125 mm is 0.25 mm shorter than theline length L when Δy=0, and the line length L of the first resonatorconductor 304 significantly varies depending on the positional deviationΔy. That is, the differential transmission line 332 according to thecomparative example is significantly affected by the positionaldeviation along the first orientation between the first resonatorconductor 304 and the pair of first via holes 105 a and 105 b. Asillustrated in FIG. 19, the center frequency of the attenuation regionin the common mode pass characteristic (Scc 21) significantly varies upand down to 3.6 GHz. Therefore, in the differential transmission line332 according to the comparative example 1, it is found that it isdifficult to inhibit the conduction propagation of the common modesignal component of the frequency (25.78 GHz) corresponding to the bitrate of the digital modulation signal by the first resonator structuredue to the manufacturing variation.

On the other hand, the first resonator conductor 104 according to thefirst embodiment extends in a linear shape to the inside of the firstresonator conductor 104 along the second orientation from each of(centers of) the land portions 110 a and 110 b at both ends. Therefore,in the pair of first via holes 105 a and 105 b (each of the centerpositions), even in a case where the positional deviation Δy withrespect to the land portions 110 a and 110 b (each of the centerpositions) along the first orientation (vertical orientation illustratedin FIG. 2) occurs, the variation of the line length L of the firstresonator conductor 104 according to the first embodiment is suppressed.Therefore, the variation of the center frequency of the attenuationregion in the common mode pass characteristic (Scc 21) of thedifferential transmission line 32 according to the first embodiment dueto the positional deviation Δy is significantly small compared to thevariation of the differential transmission line 332 according to thecomparative example.

Secondly, a case where the positional deviation Δx with respect to theland portions 110 a and 110 b (each of the center positions) occurs inthe pair of first via holes 105 a and 105 b (each of the centerpositions) along the second orientation (horizontal orientationillustrated in FIG. 2) will be considered. The variation of the linelength L of the first resonator conductor 104 according to the firstembodiment is significantly small even in a case where the positionaldeviation occurs in any direction in the second orientation. In a casewhere the position of the via hole 105 a is deviated with respect to theland portion 110 a, for example, to the right as illustrated in FIG. 2,the length of the center line along the first orientation on the side ofthe via hole 105 a decreases depending on the positional deviationamount, but the length of the center line along the first orientation onthe side of the via hole 105 b increases depending on the positionaldeviation amount, and the variation of the line length L issignificantly small. Therefore, the variation of the center frequency ofthe attenuation region in the common mode pass characteristic (Scc 21)of the differential transmission line 32 according to the firstembodiment is significantly small. In a case where the positionaldeviation Δy with respect to the first resonator conductor 304 occurs inthe pair of first via holes 105 a and 105 b according to the comparativeexample along the second orientation (horizontal orientation illustratedin FIG. 18), the variation of the line length L of the first resonatorconductor 304 according to the comparative example is small, similar tothe positional deviation Δx along the first orientation of the firstresonator conductor 104 according to the first embodiment.

In the differential transmission line 32 according to the firstembodiment, it is possible to selectively inhibit the conductionpropagation of the common mode signal component to the differentialtransmission line 32 while suppressing deterioration of the conductionpropagation of the differential signal component. That is,substantially, only the conduction propagation of the common mode signalcomponent to the differential transmission line can be selectivelyinhibited. In addition, in the formation of the first resonatorconductor 104 and the pair of first via holes 105 a and 105 b accordingto the first embodiment, an additional step is not required, and anincrease in manufacturing cost is suppressed. Furthermore, since theshape of the first resonator conductor 104 according to the firstembodiment is bent, the region where the first resonator conductor 104is disposed can be reduced, and the first resonator conductor 104 can bedisposed at a high density.

Although the dielectric layer 100 according to the first embodiment isformed using a material including a glass cloth substrate and an epoxyresin (glass epoxy resin), it is not limited to this material, and maybe a liquid crystal polymer (LCP) or a fluorine-based resin(Polytetrafluoroethylene: PTFE).

In the optical module (optical transceiver and optical transceivermodule) for optical fiber transmission, speeding up, downsizing, andcost reduction is achieved, with the spread of broadband network inrecent years, and regarding speeding up, currently the optical modulehaving a bit rate of 100 Gbit/s are widely used. Regarding downsizingand cost reduction, the housing (case) volume is reduced and the numberof parts is reduced from the CFP Multi Source Agreement (MSA) standardto CFP 2, CFP 4, and QSFP 28 (each MSA standard).

In addition, in the optical transmission equipment (network equipment)on which the optical module is mounted, it is required to suppress theintensity of unnecessary electromagnetic waves generated by theequipment to a limit value defined by law or regulations. For example,in the United States, it is required to reduce the intensity ofunnecessary electromagnetic waves below the limit value of 53.9 dB(μV/m) specified in “FCC Part 15 Subpart B” standard (in a case wheredistance is 3 m, and frequency range is 1 GHz to 40 GHz in Class Bstandard). In the optical module, unnecessary electromagnetic waves athigh frequency are generated in many cases due to switching noises orthe like of built-in IC. Therefore, a design technique for reducingradiation of the unnecessary electromagnetic waves to the outside of theequipment is important in both the optical transmission equipment andthe optical module.

In the optical module, the main excitation source of unnecessaryelectromagnetic waves is an IC (such as CDR, Driver, TIA, and the like)that amplifies and outputs an electrical serial data signal (modulationsignal). Unlike the clock signal, the ideal serial data signal does notinclude repetitive signal patterns, so that it does not have a largepeak intensity on the frequency spectrum. However, in a differentialamplifier circuit inside the actual IC, switching noise is generated dueto nonlinearity of the transistor. Therefore, in a case of observing thefrequency spectrum of the common mode component of the output signal, alarge peak occurs at the frequency corresponding to the bit rate. Whileconducting and propagating through the differential transmission line onthe print circuit board, the common mode signal component propagates tospace as apart thereof as radiation loss. As a result, since an electricserial data signal having a bit rate of 25.78 Gbit/s is used in theoptical module of 4 channels on both the transmitting side and thereceiving side at a bit rate of 100 Gbit/s, unnecessary electromagneticwaves having a frequency of 25.78 GHz corresponding to the bit rate aregenerated. In the optical module in the related art, the gap between themetal housing (metal casing) in the outer shell is further reduced, sothat the space propagation of electromagnetic waves is further shielded.Furthermore, a radio wave absorbing material is disposed inside themetal housing, so that the space propagation of electromagnetic waves isattenuated to suppress leakage of unnecessary electromagnetic waves fromthe optical transceiver.

In recent years, as the capacity of the optical transmission equipmentis increased, LSI (FPGA) having large power consumption (heat generationamount) is mounted on the optical transmission equipment. In the opticaltransmission equipment, a large number of ventilation holes are disposedto strengthen air blowing cooling, and the shielding effect of theequipment tends to be low. In addition, a plurality of optical modulesof 100 Gbit/s class are mounted on the optical transmission equipment.In the optical module conforming to the main MSA standard, for example,QSFP 28, an external connection terminal is disposed on one end of theprint circuit board, and the external connection terminal is connectedto a connector mounted on the optical transmission equipment outside themetal housing. According to this configuration, there is a problem thatunnecessary electromagnetic waves radiated from the differentialtransmission line and the connector drawn to the outside of the metalhousing are the main cause, and unnecessary electromagnetic waves of theoptical transmission equipment cannot be sufficiently suppressed.

In the optical module conforming to the QSFP 28, on a small printcircuit board having a board width of approximately 16 mm, it isrequired to dispose four pairs of differential transmission lines forthe transmitting circuit and four pairs of differential transmissionlines for the receiver circuit, respectively. The inventors have foundthat the size (length and width) of the resonator structure in therelated art requires a relatively large area to obtain a desiredresonance frequency, and it is difficult to dispose the resonatorstructure in the related art on the print circuit board of the opticalmodule conforming to the QSFP 28. On the other hand, the print circuitboard 31 according to the first embodiment has a structure suitable forsolving such a problem.

FIG. 5 is a schematic perspective view illustrating an external shape ofan optical module 2 according to the first embodiment. FIG. 6 is aschematic perspective view illustrating the structure of the opticalmodule 2 according to the first embodiment. FIG. 6 illustrates a statewhere the optical module 2 is mounted on the optical transmissionequipment 1. The print circuit board 31 according to the firstembodiment is the print circuit board 21 here.

The optical module 2 according to the first embodiment is the opticalmodule conforming to the QSFP (MSA standard). As illustrated in FIG. 5,the optical module 2 includes an upper case 200, a lower case 201, alatch 202, and a card edge connector 210. Metal such as zinc or aluminumis used as the material of the upper case 200 and the lower case 201,and a metal housing is configured to include the upper case 200 and thelower case 201. The upper case 200 and the lower case 201 configure anelectromagnetic shield by covering the print circuit board 21 in closecontact with each other so that there are no gaps in a portion otherthan the opening portion for passing the card edge connector 210. Thatis, the metal housing (upper case 200 and lower case 201) functions asan electromagnetic shield against the radiation from the print circuitboard 21 inside the metal housing. Although the metal housing has theopening portion, the metal housing functions sufficiently as theelectromagnetic shield. On the other hand, the metal housing has nofunction of preventing conduction propagation of unnecessary noisecomponents contained in the output signal from the optical module to theoptical transmission equipment. As a result, unnecessary electromagneticwaves caused by unnecessary noise components conducted and propagated tothe differential transmission line drawn out to outside of the metalhousing through the opening portion and the connector portion can beradiated to outside of the metal housing. The card edge connector 210 isan end portion of the print circuit board 21, and a plurality of contactterminals for connecting the connector are disposed in a row. The cardedge connector 210 is exposed to the outside from the opening portion(slot opening portion) on the rear sides (right side in FIG. 5) of theupper case 200 and the lower case 201, and has the function of hotswapping. The opening portion is provided to expose a portion of theprint circuit board 21 to the outside.

FIG. 6 illustrates a state where the optical module 2 is mounted on theoptical transmission equipment 1, and in order to illustrate theinternal structure of the optical module 2, a portion of the upper case200 and the lower case 201 is not illustrated. In FIG. 6, a portion ofthe print circuit board 11 and a front panel 204 inside the opticaltransmission equipment 1 are illustrated. Furthermore, a print circuitboard 11 further includes the connector 208 conforming to the QSFP 28(MSA standard), and the connector 208 is mounted on the print circuitboard 11. ROSA 23A (receiver optical subassembly), TOSA 23B (transmitteroptical subassembly: not illustrated), and flexible boards 22A and 22B(22B not illustrated) are mounted inside of the upper case 200 and thelower case 201 of the optical module 2. The print circuit board 21includes a plurality of ICs. For example, a Clock Data Recovery IC(CDR-IC) 207 on the receiving side is mounted on the print circuit board21, and the CDR-IC 207 outputs the 4-channel differential digitalmodulation signal at a bit rate of 25.78 Gbit/s. The output signal isconducted and propagated to the print circuit board 11 inside theoptical transmission equipment 1 through the four pairs of differentialtransmission lines 32 (not illustrated) disposed on the print circuitboard 21, the card edge connector 210, and the connector 208. The firstresonator structure illustrated in FIG. 2 is disposed in each of thefour pairs of differential transmission lines 32 disposed on the printcircuit board 21.

When measuring the output spectrum of the CDR-IC 207, originallyunnecessary clock noise components are observed as a peak of peak singleat a frequency of 25.78 GHz corresponding to the bit rate. However, thefirst resonator structure illustrated in FIG. 2 is disposed in each ofthe four pairs of differential transmission lines 32, so that theconduction propagation of the common mode signal component at thefrequency of 25.78 GHz can be inhibited inside the upper case 200 andthe lower case 201 of the optical module 2. Therefore, in the card edgeconnector 210, the connector 208, and the print circuit board 11 of theoptical transmission equipment 1, radiation of unnecessaryelectromagnetic waves caused by the common mode signal component can bereduced. Similarly to this mechanism, the first resonator structureillustrated in FIG. 2 is disposed on the differential transmission linedisposed on the print circuit board 11 of the optical transmissionequipment 1. Therefore, it is possible to reduce radiation ofunnecessary electromagnetic waves to the outside of the opticaltransmission equipment 1 through radiation of unnecessaryelectromagnetic waves into the inside of the optical transmissionequipment 1 and vent holes for cooling air blowing of the opticaltransmission equipment 1 and the like.

In the print circuit board 21 illustrated in FIGS. 5 and 6, the CDR-IC207 for receiving is disposed on the print circuit board 21, but it isnot limited thereto, and may be mounted in the inside of the ROSA 23A.In this case, since it is not required to dispose the CDR-IC 207 on theprint circuit board 21, the area for disposing the first resonatorconductor 104 illustrated in FIG. 2 on the print circuit board 21 can bewidely allocated to each of the four pairs of differential transmissionlines, and the degree of freedom of circuit design of the print circuitboard 21 is improved.

Second Embodiment

FIG. 7 is a schematic view illustrating a flat surface of a portion of aprint circuit board 3 l according to a second embodiment of the presentinvention. FIG. 8 is a diagram illustrating characteristics of adifferential transmission line 32 according to the second embodiment.FIG. 8 illustrates the common mode pass characteristic (Scc 21) of thedifferential transmission line 32 according to the second embodiment,and the common mode pass characteristic (Scc 21) of the differentialtransmission line 32 according to the first embodiment of the presentinvention for comparison. Although the print circuit board 31 accordingto the second embodiment is different from the first embodiment in thatthe print circuit board 31 further includes a second resonator conductor114 and second via holes 115 a and 115 b in addition to the firstresonator conductor 104, the other structure is the same as that of thefirst embodiment.

The second resonator conductor 114 is disposed in the same layer (secondmetal layer) as the first resonator conductor 104, and is provided withcircular land portions 120 a and 120 b at both ends thereof. The secondresonator conductor 114 is disposed side by side with the firstresonator conductor 104 along the first orientation (verticalorientation in FIG. 7), and the planar shape of the second resonatorconductor 114 is substantially line symmetric with the plane shape ofthe first resonator conductor 104 with respect to the straight line Xillustrated in FIG. 7. The second resonator conductor 114 extends to theoutside along the second orientation in parallel with the firstresonator conductor 104 from the portions three-dimensionallyintersecting with the pair of strip conductors 101 and 102, bends in theother direction in the first orientation (downward in FIG. 2), furtherextends away from the first resonator conductor 104 along the firstorientation, bends to the outside in the second orientation, and extendsto the outside along the second orientation to connect the pair ofsecond via holes 115 a and 115 b. Similarly to the first resonatorconductor 104, the pair of second via holes 115 a and 115 b (circularshape) are respectively disposed so that the center of the circularshape is ideally penetrated through the center of the circular shape ofthe land portions 120 a and 120 b. The pair of second via holes 115 aand 115 b connects (land portions 120 a and 120 b at the both ends of)the second resonator conductor 114 and the ground conductor layer 103,respectively. The second resonator structure is configured to includethe ground conductor layer 103, the second resonator conductor 114, andthe pair of second via holes 115 a and 115 b.

Here, in the print circuit board 32 according to the second embodiment,the distance between the centers (Via Pitch) between one first via hole(via hole 105 a) of the pair of first via holes and one second via hole(via hole 115 a) of the pair of second via holes disposed along thefirst orientation is changed. Therefore, the attenuation characteristicin the common mode pass characteristic can be adjusted. Here, thedistance between the centers (Via Pitch) is set to 2.2 mm. However, thedistance is not limited to this value, and the distance may be set to anappropriate value according to the attenuation characteristic in thecommon mode pass characteristic.

Since the first resonator conductor 104 and the second resonatorconductor 114 are disposed on the print circuit board 32 according tothe second embodiment, a wider region is required for disposing tworesonator conductors. However, as illustrated in FIG. 8, in the commonmode pass characteristic (Scc 21) of the differential transmission line32 according to the second embodiment, the attenuation region centeredat a frequency of 26.3 GHz is generated, and conduction propagation ofthe common mode signal component of the frequency of 25.78 GHz can beinhibited by approximately 20 dB. Compared to the common mode passcharacteristic (Scc 21) of the differential transmission line 32according to the first embodiment of the present invention, the commonmode pass characteristic (Scc 21) according to the second embodimentachieves greater attenuation, and the frequency range that can inhibitthe conduction propagation of the common mode signal component can bewidened.

FIG. 9 is a schematic view illustrating the flat surface of the portionof the print circuit board 31 according to the second embodiment of thepresent invention. FIG. 10 is a diagram illustrating characteristics ofthe differential transmission line 32 according to the secondembodiment. FIG. 9 illustrates a case where the positional deviation Δyoccurs with respect to the land portions 110 a and 110 b and the landportions 120 a and 120 b in any one direction of the first orientation(downward as illustrated in FIG. 9) in the pair of first via holes 105 aand 105 b and the pair of second via holes 115 a and 115 b in the printcircuit board 31 illustrated in FIG. 7. Here, the positional deviationΔy is −0.125 mm. FIG. 10 illustrates the common mode pass characteristic(Scc 21) of the differential transmission line 32 (Δy=0) illustrated inFIG. 9, and the common mode pass characteristic (Scc 21) of thedifferential transmission line 32 (Δy=±0.125 mm) illustrated in FIG. 7for comparison. Since the planar shape of the first resonator conductor104 and the planar shape of the second resonator conductor 114 are linesymmetric with respect to the straight line X, even if any positionaldeviation in any one direction of the first orientation (upward ordownward in FIG. 9) occurs, if the absolute values are the same, theobtained common mode passing characteristic (Scc 21) is substantiallythe same. As illustrated in FIG. 10, even in a case where the positionaldeviation Δy occurs (Δy=±0.125 mm), although the center frequency of theattenuation region in the common mode pass characteristic (Scc 21)varies to a frequency lower by approximately 0.5 GHz, the conductionpropagation of the common mode signal component can be inhibited byapproximately 20 dB at the frequency of 25.78 GHz.

Third Embodiment

FIG. 11 is a schematic view illustrating a flat surface of a portion ofa print circuit board 31 according to a third embodiment of the presentinvention. FIG. 12 is a diagram illustrating characteristics of adifferential transmission line 32 according to the third embodiment.FIG. 12 illustrates the common mode pass characteristic (Scc 21) of thedifferential transmission line 32 according to the third embodiment, andthe common mode pass characteristic (Scc 21) of the differentialtransmission line 32 according to the first embodiment of the presentinvention for comparison. Although in the print circuit board 31according to the third embodiment, the shape of the second resonatorconductor 114 is different from that of the second embodiment, the otherstructure is the same as that of the second embodiment.

In the second embodiment, the planar shape of the second resonatorconductor 114 is substantially line symmetric with the plane shape ofthe first resonator conductor 104 with respect to the straight line Xillustrated in FIG. 7, whereas in the third embodiment, the planar shapeof the second resonator conductor 114 substantially coincides with theone obtained by translating the planar shape of the first resonatorconductor 104 in any one direction of the first orientation (downward inFIG. 11). The second resonator conductor 114 extends to the outsidealong the second orientation in parallel with the first resonatorconductor 104 from the portions three-dimensionally intersecting withthe pair of strip conductors 101 and 102, bends in any one direction ofthe first orientation (downward in FIG. 2), further extends in the samedirection as the first resonator conductor 104 along the firstorientation, bends to the outside in the second orientation, and extendsto the outside along the second orientation to connect with the pair ofsecond via holes. Similarly to the second embodiment, the pair of secondvia holes 115 a and 115 b (circular shape) are respectively disposed sothat the center of the circular shape is ideally penetrated through thecenter of the circular shape of the land portions 120 a and 120 b. Thepair of second via holes 115 a and 115 b connects (land portions 120 aand 120 b at the both ends of) the second resonator conductor 114 andthe ground conductor layer 103, respectively. The second resonatorstructure is configured to include the ground conductor layer 103, thesecond resonator conductor 114, and the pair of second via holes 115 aand 115 b.

Similarly to the second embodiment, in the print circuit board 32according to the third embodiment, the distance between the centers (ViaPitch) between one first via hole (via hole 105 a) of the pair of firstvia holes and one second via hole (via hole 115 a) of the pair of secondvia holes disposed along the first orientation is changed. Therefore,the attenuation characteristic in the common mode pass characteristiccan be adjusted. Here, the distance between the centers (Via Pitch) isset to 1.2 mm. However, the distance is not limited to this value, andthe distance may be set to an appropriate value according to theattenuation characteristic in the common mode pass characteristic.

Since the first resonator conductor 104 and the second resonatorconductor 114 are disposed on the print circuit board 32 according tothe third embodiment, a wider region is required for disposing tworesonator conductors. However, as illustrated in FIG. 12, in the commonmode pass characteristic (Scc 21) of the differential transmission line32 according to the third embodiment, the attenuation region centered ata frequency of 26.3 GHz is generated, and conduction propagation of thecommon mode signal component of the frequency of 25.78 GHz can beinhibited by approximately 20 dB. Compared to the common mode passcharacteristic (Scc 21) of the differential transmission line 32according to the first embodiment of the present invention, the commonmode pass characteristic (Scc 21) according to the third embodimentachieves greater attenuation, and the frequency range that can inhibitthe conduction propagation of the common mode signal component can bewidened.

Fourth Embodiment

FIG. 13 is a schematic view illustrating a structure of a portion of aprint circuit board 31 according to a fourth embodiment of the presentinvention. Although in the print circuit board 31 according to thefourth embodiment, the shape of the first resonator conductor 104 isdifferent from that of the first embodiment, the other structure is thesame as that of the first embodiment. The first resonator conductor 104according to the first embodiment extends in a linear shape from each of(centers of) the land portions 110 a and 110 b at both ends along thesecond orientation to the inside of the first resonator conductor 104,whereas the first resonator conductor 104 according to the fourthembodiment extends in a linear shape from each of (centers of) the landportions 110 a and 110 b at both ends along the second orientation tothe outside of the first resonator conductor 104. That is, the firstresonator conductor 104 according to the fourth embodiment extends fromeach of (centers of) the pair of first via holes 105 a and 105 b alongthe second orientation to the outside of the first resonator conductor104.

When the directions respectively extending from both ends of the firstresonator conductor 104 extends are referred to as a first extendingdirection and a second extending direction, and in the first to thirdembodiments (and the fifth to seventh embodiments), the first extendingdirection and the second extending direction are opposed to each otheron a straight line, and the angle between the first extending directionand the second extending direction is 180°. In the fourth embodiment,the first extending direction and the second extending direction tend toseparate from each other on the straight line, and the angle between thefirst extending direction and the second extending direction is 180°.The first extending direction and the second extending direction may beeither opposed to each other (facing inward) or separate away from eachother (facing outward) along the second direction, and in either case,it is possible to reduce the variation of the line length L with respectto the positional deviation Δx along the second orientation.

It is desirable that both of the first resonator conductor 104 accordingto the fourth embodiment extend along the second orientation from bothends thereof (land portions 110 a and 110 b) or from each of the pair offirst via holes 105 a and 105 b to the outside of the first resonatorconductor 104, and that both further bend in any one direction in thefirst orientation (downward in FIG. 13). Furthermore, it is desirablethat both extend to the inside of the first resonator conductor 104along the second orientation, and reach the portions three-dimensionallyintersecting with the pair of strip conductors 101 and 102. That is, itis desirable that the first resonator conductor 104 extends to theoutside along the second orientation from the portionsthree-dimensionally intersecting with the pair of strip conductors 101and 102, bends in any one direction in the first orientation (upward inFIG. 2), further extends along the first orientation, bends to theinside in the second orientation, and extends to the inside along thesecond orientation to connect with the pair of first via holes.

The distance D between the centers of the pair of first via holes 105 aand 105 b is 1.1 mm and the width W₁ of the first resonator conductor104 is 0.20 mm. Although the first resonator conductor 104 has a linearshape portion to be extended and a bending portion, for impedancematching, the corner of the bending portion has a cut off shape. Thelength L₁ of the center line is 0.45 mm. Even with the print circuitboard 31 according to the fourth embodiment, the same effects as thoseof the first embodiment is achieved.

Fifth Embodiment

FIG. 14 is a schematic view (perspective view) illustrating a structureof a portion of a print circuit board 31 according to a fifth embodimentof the present invention. Although in the print circuit board 31according to the fifth embodiment, the shape of the first resonatorconductor 104 is different from that of the first embodiment, the otherstructure is the same as that of the first embodiment.

The first resonator conductor 104 according to the first embodiment hasthe bending portion, whereas the first resonator conductor 104 accordingto the fifth embodiment extends in a linear shape to the inside of thefirst resonator conductor 104 from both (centers of) the land portions110 a and 110 h at both ends along the second orientation, and reachesthe portions three-dimensionally intersecting with the pair of stripconductors 101 and 102. That is, it is desirable that the firstresonator conductor 104 extends to the outside along the secondorientation from the portions three-dimensionally intersecting with thepair of strip conductors 101 and 102 to connect with the pair of firstvia holes.

The first resonator conductor 104 according to the fifth embodimentextends in a linear shape except for the land portions 110 a and 110 bon both sides. The distance between the centers D between the pair offirst via holes 105 a and 105 b is 3.05 mm. The width W₁ of the firstresonator conductor 104 is 0.19 mm. Although the first resonatorconductor 104 is formed into a linear shape, so that the distancebetween the centers D is longer, the resonator structure can be realizedwith a significantly simple configuration.

Sixth Embodiment

FIG. 15 is a schematic view (perspective view) illustrating a structureof a portion of a print circuit board 31 according to a sixth embodimentof the present invention. Although in the print circuit board 31according to the sixth embodiment, the shape of the first resonatorconductor 104 and the shape of the second resonator conductor 114 aredifferent from these of the second and third embodiment, the otherstructure is the same as these of the second and third embodiment.

Each of the first resonator conductor 104 and the second resonatorconductor 114 according to the second and third embodiments has thebending portion, whereas each of the first resonator conductor 104 andthe second resonator conductor 114 according to the sixth embodimentextends in a linear shape to the inside of the first resonator conductor104 from each of the land portions at both ends along the secondorientation, and reaches the portions three-dimensionally intersectingwith the pair of strip conductors 101 and 102. That is, it is desirablethat the first resonator conductor 104 and the second resonatorconductor 114 extend to the outside along the second orientation fromthe portions three-dimensionally intersecting with the pair of stripconductors 101 and 102 to connect with the pair of first via holes andthe pair of second via holes.

The first resonator conductor 104 and the second resonator conductor 114according to the sixth embodiment extend in a linear shape except forthe land portions on both sides. The distance between the centers Dbetween the pair of first via holes 105 a and 105 b and the distancebetween the centers D between the pair of second via holes 115 a and 115b are both 3.05 mm. The width W₁ of the first resonator conductor 104 is0.19 mm. Although the first resonator conductor 104 and the secondresonator conductor 114 are formed into the linear shapes, so that thedistances between the centers D are longer, the resonator structures canbe realized with the significantly simple configurations.

Seventh Embodiment

FIG. 16 is a schematic view (perspective view) illustrating a structureof a portion of a print circuit board 31 according to a seventhembodiment of the present invention. FIG. 17 is a schematic viewillustrating a cross section of the portion of the print circuit board31 according to the seventh embodiment. Although in the print circuitboard 31 according to the seventh embodiment, the shapes of the firstresonator conductor 104 and the pair of first via holes 105 a and 105 bare different from these of the fifth embodiment, the other structure isthe same as that of the fifth embodiment.

Although the planar shape of the first resonator conductor 104 accordingto the seventh embodiment coincides with the planar shape of the firstresonator conductor 104 according to the fifth embodiment, asillustrated in FIG. 17, in the multi layer structure of the printcircuit board 31, the first resonator conductor 104 according to theseventh embodiment is disposed in the uppermost metal layer, and thepair of strip conductors 101 and 102 according to the seventh embodimentare disposed in the second metal layer. That is, the first resonatorconductor 104 is disposed on the board surface side in the laminationorientation of the ground conductor layer 103, and the pair of stripconductors 101 and 102 are disposed between the first resonatorconductor 104 and the ground conductor layer 103. The first resonatorconductor 104 is disposed on the board surface side in the laminationorientation of the pair of strip conductors 101 and 102. The pair offirst via holes 105 a and 105 b connects (land portions 110 a and 110 bat both ends of) the first resonator conductor 104 and the groundconductor layer 103, respectively.

Here, the distance H₁ between the pair of strip conductors 101 and 102and the ground conductor layer 103 is 138 μm, and the distance H₂between the pair of strip conductors 101 and 102 and the first resonatorconductor 104 is 65 μm. As described above, the distance H₁ is desirablytwice or more the distance H₂, and the print circuit board 31 accordingto the seventh embodiment satisfies such a condition. The width W of thepair of strip conductors 101 and 102 is 0.20 mm, and the interval Gbetween the pair of strip conductors 101 and 102 is 0.20 mm. Thedistance between the centers D of the pair of first via holes 105 a and105 b is 3.05 mm, and the width W₁ of the first resonator conductor 104is 0.19 mm.

Although in the print circuit board 31 according to the seventhembodiment, the layer on which the first resonator conductor 104 isdisposed is different from these of the print circuit boards 31according to the first to sixth embodiments, the print circuit board 31according to the seventh embodiment has the same effects as that of thefirst embodiment. The configuration in which the first resonatorconductor 104 and the second resonator conductor 114 are disposedfurther above the pair of strip conductors 101 and 102 is not limited tothe seventh embodiment, and may be applied to each of the second tosixth embodiments.

Hereinbefore, the print circuit board, the optical module, and theoptical transmission equipment according to the embodiments of thepresent invention are described. The present invention is not limited tothe above embodiments and may be widely applied to a print circuit boardhaving a resonator structure and a differential transmission line of amicro-strip line type. Although the print circuit board according to thepresent invention is the print circuit board provided in the opticaltransmission equipment and the optical module, the print circuit boardmay be provided in another equipment. In addition, although in the printcircuit board according to the embodiments of the present invention, thecase where the bit rate of the digital electric signal transmittedthrough each channel is 25.78 Gbit/s is described, it is not limited tosuch a bit rate and is suitable for a further higher bit rate.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A printed circuit board comprising: a groundconductor layer; a pair of strip conductors disposed on a board surfaceside of the ground conductor layer and extending along a firstorientation; a resonator conductor disposed between the ground conductorlayer and the pair of strip conductors, wherein the resonator conductorcomprises a first circular land portion and a second circular landportion, wherein the resonator conductor comprises a linear shapeextending along a second orientation across the pair of stripconductors, and wherein the linear shape has a first dimension in thefirst orientation and a second dimension in the second orientation, thesecond dimension being longer than the first dimension; a pair of viaholes connecting the resonator conductor and the ground conductor layer;and a dielectric layer disposed between the ground conductor layer andthe pair of strip conductors, wherein the resonator conductor isdisposed inside the dielectric layer, and wherein a differentialtransmission line of a micro-strip line type in which a digitalmodulation signal is transmitted is configured by the ground conductorlayer, the pair of strip conductors, and the dielectric layer.
 2. Theprinted circuit board of claim 1, further comprising: a dielectric filmcovering an uppermost layer of the printed circuit board, wherein thepair of strip conductors are disposed between the dielectric film andthe dielectric layer.
 3. The printed circuit board of claim 1, wherein adistance between the pair of strip conductors and the ground conductorlayer is twice or more a distance between the pair of strip conductorsand the resonator conductor.
 4. The printed circuit board of claim 1,wherein the resonator conductor comprises the linear shape extendingfrom a first via hole, of the pair of via holes, towards a second viahole, of the pair of via holes, along the second orientation across thepair of strip conductors.
 5. The printed circuit board of claim 1,wherein a first portion of the resonator conductor comprises the linearshape extending along the second orientation across the pair of stripconductors; wherein a second portion of the resonator conductor extendsfrom a first via hole, of the pair of via holes, towards a second viahole of the pair of via holes along the second orientation, and bends ina direction along the first orientation; and wherein a third portion ofthe resonator conductor extends from the second via hole towards thefirst via hole along the second orientation, and bends in the directionalong the first orientation.
 6. The printed circuit board of claim 5,wherein the first portion connects the second portion and the thirdportion.
 7. The printed circuit board of claim 1, wherein a firstportion of the resonator conductor comprises the linear shape extendingalong the second orientation across the pair of strip conductors;wherein a second portion of the resonator conductor extends from a firstvia hole, of the pair of via holes, and away from a second via hole ofthe pair of via holes along the second orientation, and bends in adirection along the first orientation; and wherein a third portion ofthe resonator conductor extends from the second via hole and away fromthe first via hole along the second orientation, and bends in thedirection along the first orientation.
 8. The printed circuit board ofclaim 7, wherein the first portion connects the second portion and thethird portion.
 9. The printed circuit board of claim 1, wherein theresonator conductor comprises the linear shape extending from the firstcircular land portion towards the second circular land portion along thesecond orientation across the pair of strip conductors.
 10. The printedcircuit board of claim 1, wherein a first portion of the resonatorconductor comprises the linear shape extending along the secondorientation across the pair of strip conductors; wherein a secondportion of the resonator conductor extends from the first circular landportion towards the second circular land portion along the secondorientation and bends in a direction along the first orientation; andwherein a third portion of the resonator conductor extends from thesecond circular land portion towards the first circular land portionalong the second orientation and bends in the direction along the firstorientation.
 11. The printed circuit board of claim 10, wherein thefirst portion connects the second portion and the third portion.
 12. Theprinted circuit board of claim 1, wherein a first portion of theresonator conductor comprises the linear shape extending along thesecond orientation across the pair of strip conductors; wherein a secondportion of the resonator conductor extends from the first circular landportion and away from the second circular land portion along the secondorientation, and bends in a direction along the first orientation; andwherein a third portion of the resonator conductor extends from thesecond circular land portion and away from the first circular landportion along the second orientation, and bends in the direction alongthe first orientation.
 13. The printed circuit board of claim 12,wherein the first portion connects the second portion and the thirdportion.
 14. The printed circuit board of claim 1, wherein a resonatorstructure is configured to include the ground conductor layer, theresonator conductor, and the pair of via holes.
 15. A printed circuitboard comprising: a ground conductor layer; a pair of strip conductorsdisposed to extend along a first orientation; a resonator conductordisposed on a board surface side of the printed circuit board, whereinthe pair of strip conductors are disposed between the resonatorconductor and the ground conductor layer, wherein the resonatorconductor comprises a linear shape extending along a second orientationacross the pair of strip conductors, and wherein the linear shape has afirst dimension in the first orientation and a second dimension in thesecond orientation, the second dimension being longer than the firstdimension; a pair of via holes connecting the resonator conductor andthe ground conductor layer; and a dielectric layer disposed between theground conductor layer and the pair of strip conductors, wherein adifferential transmission line of a micro-strip line type in which adigital modulation signal is transmitted is configured by the groundconductor layer, the pair of strip conductors, and the dielectric layer.16. The printed circuit board of claim 15, wherein the resonatorconductor comprises the linear shape extending from a first via hole, ofthe pair of via holes, towards a second via hole, of the pair of viaholes, along the second orientation across the pair of strip conductors.17. The printed circuit board of claim 15, wherein a first portion ofthe resonator conductor comprises the linear shape extending along thesecond orientation across the pair of strip conductors; wherein a secondportion of the resonator conductor extends from a first via hole, of thepair of via holes, and away from a second via hole of the pair of viaholes along the second orientation, and bends in a direction along thefirst orientation; and wherein a third portion of the resonatorconductor extends from the second via hole and away from the first viahole along the second orientation, and bends in the direction along thefirst orientation.
 18. The printed circuit board of claim 17, whereinthe first portion connects the second portion and the third portion. 19.The printed circuit board of claim 15, wherein the resonator conductorcomprises a first circular land portion and a second circular landportion.
 20. The printed circuit board of claim 19, wherein a firstportion of the resonator conductor comprises the linear shape extendingalong the second orientation across the pair of strip conductors;wherein a second portion of the resonator conductor extends from thefirst circular land portion and away from the second circular landportion along the second orientation, and bends in a direction along thefirst orientation; wherein a third portion of the resonator conductorextends from the second circular land portion away from the firstcircular land portion along the second orientation, and bends in thedirection along the first orientation; and wherein the first portionconnects the second portion and the third portion.